Microwave power adder circuit



MarCh 18, 1969 I 1 H O'BmEN ET AL 3,434,148

MICROWAVE POWER ADDER CIRCUIT Filed Aug. l, 1966 Sheet of P BLW z| N 1 &|\ m f2 2 C w g sj Lawrence H. O'Brien,

2 m Richard S. Jomlson, g`- {i} INVENToRs. ui g Y %W%M ATTORNEY.

March 18, 1969 L. H. OBRIEN ET AL- MICROWAVE POWER ADDER CIRCUIT Filed Aug. i, 196e Loss in radiated power in decibels.

Sheet ofz O.| 0.5 I 2 5 IO 50 |00 Difference in power between Transmitters A a B in decibels.

F i g. 2.

Lawrence H. O'Brien,

Richard S. Jamison,

|NvENToRs.

.Y ATTCRNY- United States Patent C) 6 Claims This invention relates to a coherent microwave power addition circuit and more particularly to an improved coherent microwave addition circuit 4which provides higher average power than conventional circuits without increasing the peak power in the waveguide or increasing the duty cycle.

Substantial diiculty has been encountered in developing techniques of adding coherent microwave energy. One basic technique previously tried has been the direct power addition of microwave energy via series directional couplers. However, when utilizing the directional coupler arrangement, the peak power is limited by power handling capability of the waveguide. Another technique is a multiple antenna feed arrangement. However, precise phase control must be maintained or else beam steering problems are introduced which result in unsatisfactory operation.

It is, therefore, an object of this invention to provide an improved power Vaddition circuit which provides a higher average power than conventional circuits without increasing the peak power in any one section of waveguide or increasing the duty cycle.

It is a further object of this invention to provide an improved power addition circuit wherein precise phase control of the power to be combined is not critical.

It is a still further object of this invention to provide an improved circuit -which does not have inherent beam steering problems.

Briefly, in accordance with the objects set forth above, one embodiment of the coherent microwave power addition circuit according to the present invention comprises a first set of two magic tees, each one being receptive to different, but coherent, sources of microwave energy. The coherent input signals are divided in the first two magic tees and portions of each input are then recombined in a second set of magic tees. The outputs from the second set of magic tees travel to respective circulators and then the outputs are utilized to excite a conventional monopulse antenna.

Additional objects, advantages and characteristic features of the present invention will become readily apparent from the following detailed description of the preferred embodiment of the invention when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a `schematic of a microwave power adder circuit in accordance with the present invention; and

FIG. 2 is a graph illustrating a family of curves which represent the loss in radiated power versus the difference in power and/ or phase between the two transmitters utilized in accordance with the present invention.

Referring now to FIG. 1, a microwave power adder circuit is shown. Essentially, the circuit comprises two paths wherein the input signals from two coherent microwave transmitters 24 and 25 are added together and then fed to an antenna 23, which may be a conventional monopulse antenna. The coherent transmitters utilized in circuit 10 may be any of a number of conventional transmitters depending upon the frequency and power requirements of the system. Furthermore, any multiple of two transmitters, such as, four or six transmitters, may be utilized in accordance with the present invention depending upon the linal output power desired.

In order to have optimum power addition, the output ice from the transmitters must be coherent, that is, the outputs from the two transmitters must bear a constant frequency and phase relationship to each other. However, for the purpose of explanation of FIG. 2, the aforementioned input signals from the two transmitters are designated aS A qb and B0. One of the systems constructed and tested by the applicant was within the Ku band and the family of curves illustrated in FIG. 2 reliect the results obtained. The particular equipment referred to throughout this application was utilized in the construction of a system ernployed within the Ku band. However, the microwave power adder circuit 10 may be employed within other frequency limits and the utility of the circuit 10 has been demonstrated within other frequency limits, such as, the X-band.

Referring again to FIG. l, in the upper path a rotary means 11, which may Ibe a set of conventional rotary joints, is receptive to an input signal from a transmitter A. The output voltage A qb from the rotary means 11 travels to a magic tee 13, which is a conventional microwave hybrid junction, such as, a 62TH42A manufactured by Microwave Development Laboratories. The shunt arms of the magic tee 13 are connected symmetrically and the arms are series terminated; therefore, the junction is reflectionless for the input signal A qb. Thus, the output voltages from the magic tee 13 are a5, and il: ,/2 ,/2

respectively, as shown. In the lower path, which includes a Irotary means 12 and magic tee 14, both being of the same type as utilized in the upper path, the same process takes place with regard to an input signal B 0, as shown in FIG. 1.

A second set of magic tees 15 and 16 are utilized to add portions of the input signals A and B0. The magic tees 15 and 16 are conventional microwave hybrid junctions, such as, a 62TN26A manufactured by Microwave Development Laboratories. The output voltage of the magic tee 15 is as is the output voltage of the magic tee 16. The outputs from the ma-gic tees 1S and 16 are applied to the circulators 17 and 18, respectively. The circulators 17 and 18 are conventional non-reciprocal devices, such as, a D291H manufactured by Ferrotec Incorporated. The respective outputs from the circulators 17 and 18 are fed into the junctions 19 and 20, which may be conventional hybrid junctions, such as, a 62TN26A manufactured by Microwave Development Laboratories. The respective outputs of the junctions 19 and 20 are then fed to the antenna 23 via inputs 23A through D. The junctions 21 and 22 are also conventional hybrid junctions similar to the junctions 19 and 20. The three outputs from the junctions 21 and 22 are utilized to provide the sum signal, the azimuth error, and the elevation error information upon the return of a portion of the transmitted energy. Further discussion of conventional monopulse radar systems may be found in Introduction to Radar Systems, by M. I. Skolnik, 1962, McGraw Hill Company, pp. -184.

It is noted that the original input signals, A and B 0, are split, and re-added in such a manner that the antenna illumination is shared equally by `both transmitters. The partial failure of either transmitter or its associated circuitry will have an effect of reducing overall input power. However, such a failure Will not shift the position of the beam radiated by the antenna 23. Thus, any possibility of beam steering is eliminated because of the self-compensating effects. Furthermore, this power combination technique limits the waveguide power to a value which never exceeds the peak power input power of any individual transmitter. Thus, in comparison to conventional microwave power adder circuits, the microwave power adder circuit 10, while utilizing conventional waveguide size, allows the peak power output at the antenna 23 to be increased. As stated earlier, any multiple of two transmitters may be utilized in the practice of this invention with the resulting effect of increased output power. The outputs from the transmitters may be divided and combined in the same manner as A qb and B 0, so that antenna illumination is shared equally by all transmitters.

Referring now to FIG. 2, the graph 30 illustrates the family of curves which represent the loss in radiated power versus the difference in power and/or phase between two transmitters A and B. While the graph 30 reflects results obtained utilizing the coherent addition of the outputs from a pair of SFD-220 high power amplifiers operating within the Ku band, it should be understood that the practice of this invention is not necessarily limited thereto, but may 4be practiced to equal advantage utilizing other power amplifiers within other frequency limits, for example, a pair of SFD-218 power amplifiers operating within the X-band. The family of curves of the graph 30 include curves illustrating the effects of a zero to 90 phase difference between transmitter A and transmitter B.

Since the upper and lower paths of FIG. 1 are symmetrical, the voltage output from the magic tees and 16 are identical and equal to and the voltage at the terminated ports is equal to From these relationships it can be seen that for equal amplitude and zero relative phase difference, i.e., A=B and =0, respectively, the power of each magic tee 15 and 16 is equal to (A/Z-j-B/2)2=A2 while the power lost in the terminations is equal to (A/2-B/2)2=0. As an illustrative example, suppose the failure of a rotary joint dropped the power in path A 2 db and caused a 30 degree phase shift. The overall effect is shown by the following calculation.

As shown in graph 30, the point X indicates that for a 2 db power drop resulting from a failure in either transmitter or its associated circuitry combined with a phase error of 30, the transmitted signal would sustain an overall loss in radiated power of 1.25 db.

Thus, although the present invention has been shown and described with reference to particular embodiments, nevertheless, various changes and modifications obvious to a person skilled in the art to which the invention pertains are deemed to lie within the spirit, scope, and contemplation of the invention as set forth in the appended claims.

What is claimed is:

1. A microwave power adder circuit comprising:

first hybrid junction means for dividing a first electromagnetic wave signal equally between first and second signal paths and for dividing a second electromagnetic wave signal equally between third and fourth signal paths;

second hybrid junction means coupled to said first hybrid junction means for combining the electromagnetic wave signals of said first and third signal paths to form a first combined electromagnetic wave signal and for combining the electromagnetic wave signals of said second and fourth signal paths to form a second combined electromagnetic wave signal;

non-reciprocal means coupled to said second hybrid junction means for providing respective signal paths for said first combined electromagnetic wave signal and for said second electromagnetic wave signal; and

third hybrid junction means coupled to said non-reciprocal means for dividing said first and second combined electromagnetic wave signals.

2. A microwave power adder circuit comprising:

first hybrid junction means for dividing first electromagnetic wave signals equally between two n number of signal paths, where n is any integer not less than one, and for dividing second electromagnestic wave signals equally between nl number of signal paths, where nl is an integer not less than l;

second hybrid junction means coupled to said first lhybrid junction means for combining the electromagnetic wave signals of said n number of signal paths to form a first combined electromagnetic wave signal and for combining the electromagnetic wave signals of said nl number of signal paths to form a second combined electromagnetic wave signal;

non-reciprocal means coupled to said `second hybrid junction means for providing respective signal paths for said first combined electromagnetic wave signal and said second electromagnetic wave signal; and

third `hybrid junction means coupled to said non-reciprocal means for dividing said first and second combined electromagnetic wave signals.

3. A microwave power adder circuit comprising:

first hybrid junction means having a first input adapted to receive a first electromagnetic wave signal and first and second output ports for dividing said first electromagnetic wave signal equally between said -first and second output ports of said first hybrid junction means;

second hybrid junction means having a first input port adapted to receive a second electromagnetic wave signal and first and second ouput ports for dividing said second electromagnetic wave signal equally between said first and second output ports of said second hybrid junction means;

third hybrid junction means having first and second input ports coupled to the respective first output ports of said first and second :hybrid junction means for combining the outputs from said ports, said third hybrid junction means having an output port;

fourth hybrid junction means having first and second input ports coupled to the respective second output ports of said first and second hybrid junction means for combining the outputs from said ports, said fourth hybrid junction means having an output port;

a first path coupled to said output port of said third hybrid junction means, including means for circulating and means for dividing a portion of said combined first and second electromagnetic wave signals from said output ports of said third ihybrid junction means;

a second path coupled to said output port of said fourth hybrid junction means, including means for circulating and means for dividing a portion of said combined first and second electromagnetic wave signals from said output port of said fourth hybrid junction means; v

fifth hybrid junction means coupled between said first and second paths for coupling a portion of said cornbined first and second elctromagnetic wave signals; and

sixth hybrid junction means coupled between said first and seco-nd paths for coupling a portion of said first and second electromagnetic signals.

4. A microwave power adder circuit receptive to electromagnetic wave signals from first and second microwave energy sources and adapted to feed electromagnetic wave signals to an antenna, said circuit further adapted to receive electromagnetic wave signals from said antenna, said circuit comprising:

first rotary means for receiving electromagnetic wave signals from said first microwave energy source; first hybrid junction means coupled to said first rotary means for dividing said electromagnetic waive signals from said `first rotary means equally between rst and second output ports of said first hybrid junction means;

second rotary means for receiving electromagnetic wave signals from said second microwave energy source;

second hybrid junction means coupled to said second rotary means for dividing electromagnetic wave signals from said second rotary means equally between first and second output ports of said second hybrid junction means;

third hybrid junction means coupled to the respective first ports of said first and second hybrid junction means for combining the electromagnetic wave signals from said ports;

fourth hybrid junction means coupled to the respective second ports of said first and `second Ihybrid junction means for combining the electromagnetic wave signals from said ports;

fifth hybrid junction means connected to said antenna for coupling electromagnetic wave signals to and from said antenna;

sixth hybrid junction means connected to said antenna for coupling electromagnetic yWave signals to and from said antenna;

-seventh hybrid junction means coupled between said fifth and sixth hybrid junction means for coupling electromagnetic wave signal from said antenna;

first non-reciprocal means coupled between said third and -fifth hybrid junction means for coupling electromagnetic wave signals to and from said fifth hybrid junction means;

second non-reciprocal means coupled between said fourth and sixth 'hybrid junction means for coupling the electromagnetic wave signals to and from said sixth hybrid junction means; and

eighth hybrid junction means connected between said first and second non-reciprocal means for coupling electromagnetic wave signals from said antenna.

5. Apparatus as set forth in claim 4 wherein said first and second non-reciprocal means are circulators.

6. A microwave power adder circuit comprising:

first rotary means for receiving a first electromagnetic wave signal;

first hybrid junction means having an input port coupled to s'aid first rotary means for dividing said first electromagnetic wave signal equally between first and second output ports of said first hybrid junction means;

second rotary means for receiving a second electro magnetic wave signal;

second hybrid junction means having an input port coupled to said second rotary means for dividing said second electromagnetic wave signal from said second rotary means equally between first and second output ports of said second hybrid means;

third hybrid junction means coupled to the respective first output ports of said first and second hybrid junction means for combining the outputs from said ports;

fourth hybrid junction means coupled to the respective second output ports of said first and second hybrid junction means for combining the outputs from said ports;

first circulator means having a first port coupled to the output port of said third hybrid junction means for providing a signal path for the electromagnetic wave signal from said output port;

second circulator means having a first port coupled to the output port of said fourth hybrid junction means for providing a signal path for the electromagnetic wave signals from said output port;

fifth hybrid junction means coupled to a second port of said first circulating means for providing a signal path for electromagnetic wave signals;

sixth hybrid junction means coupled to a second port of said second circulating means for providing a signal path for electromagnetic wave signals;

seventh hybrid junction means coupled between respective third ports of said first and second circulating means for providing a signal path for electromagnetic wave signals; and

eighth hybrid junction means coupled 'between said fifth and sixth hybrid junction means for providing a signal path for electromagnetic wave signals.

References Cited UNITED STATES PATENTS 3,392,395 7/1968 Hannan 343-777 ELI LIEBERMAN, Primary Examiner.

U.S. Cl. X.R. 

1. A MICROWAVE POWER ADDER CIRCUIT COMPRISING: FIRST HYBRID JUNCTION MEANS FOR DIVIDING A FIRST ELECTROMAGNETIC WAVE SIGNAL EQUALLY BETWEEN FIRST AND SECOND SIGNAL PATHS AND FOR DIVIDING A SECOND ELECTROMAGNETIC WAVE SIGNAL EQUALLY BETWEEN THIRD AND FOURTH SIGNAL PATHS; SECOND HYBIRD JUNCTION MEANS COUPLED TO SAID FIRST BYBIRD JUNCTION MEANS FOR COMBINING THE ELECTROMAGNETIC WAVE SIGNALS OF SAID FIRST AND THIRD SIGNAL PATHS TO FORM A FIRST COMBINED ELECTROMAGNETIC WAVE SINGAL AND FOR COMBINING THE ELECTROMAGNETIC WAVE SIGNALS OF SAID SECOND AND FOURTH SIGNAL PATHS TO FROM A SECOND COMBINED ELECTROMAGNETIC WAVE SIGNAL; NON-RECIPROCAL MEANS COUPLED TO SAID SECOND HYBIRD JUNCTION MEANS FOR PROVIDING RESPECTIVE SIGNAL PATHS FOR SAID FIRST COMBINED ELECTROMAGNETIC WAVE SIGNAL AND FOR SAID SECOND ELECTROMAGNETIC WAVE SIGNAL; AND THIRD HYBIRD JUNCTION MEANS COUPLED TO SAID NON-RECIPROCAL MEANS FOR DIVIDING SAID FIRST AND SECOND COMBINED ELECTROMAGNETIC WAVE SIGNALS. 